5G NR Transport Block Size (TBS) Calculator

The 5G NR TBS Calculator calculates the Transport Block Size (TBS) for a 5G New Radio transmission based on allocated resource elements, modulation order, target code rate, and MIMO spatial layers. It first calculates the unquantized information size and then applies the TBS quantization logic used by the calculator implementation.

Transport Block Size is an important physical-layer parameter because it determines how many information bits can be carried in a transport block for a particular transmission configuration. Understanding TBS helps engineers analyze 5G NR capacity, throughput, MIMO performance, modulation efficiency, and resource allocation.

The calculator provides several useful outputs, including unquantized information bits, quantized TBS in bits and bytes, modulation scheme, MIMO layers, and an estimated throughput based on a 30 kHz subcarrier-spacing assumption.

What Is Transport Block Size (TBS) in 5G NR?

Transport Block Size (TBS) is the number of information bits contained in a transport block used for a 5G NR transmission. It is an important link between higher-layer data scheduling and the physical-layer transmission process.

A transport block can contain user data that is prepared for transmission over the NR physical channel. Before transmission, the data is processed through channel coding and other physical-layer operations.

TBS is affected by several transmission parameters, including:

• The amount of allocated radio resources
• Modulation order
• Target code rate
• Number of MIMO spatial layers
• TBS quantization and code-block processing rules

A simplified starting point for calculating the information size is:

N_info = N_RE × Q_m × R × v

Where:

• N_RE = allocated resource elements
• Q_m = modulation order in bits per symbol
• R = target code rate
• v = number of MIMO spatial layers
• N_info = unquantized information-bit estimate

However, this calculation does not directly give the final TBS in every case. The calculator subsequently applies the appropriate TBS quantization procedure.

Why Does TBS Matter?

TBS is useful when analyzing:

• 5G NR downlink capacity
• 5G NR uplink capacity
• MIMO transmission
• Modulation and coding
• Radio resource allocation
• Link adaptation
• Theoretical throughput
• Network simulation
• 5G physical-layer performance

For example, increasing the number of resource elements or MIMO layers can increase the calculated information capacity. Similarly, using a higher modulation order can increase the number of bits represented by each modulation symbol.

How the 5G NR TBS Calculator Works

The calculator follows a multi-step process rather than treating the simple multiplication formula as the final answer.

The general calculation flow is:

Resource Elements → N_info → TBS Quantization → Final TBS → Bytes → Estimated Throughput

Step 1: Calculate Unquantized Information Bits

The calculator starts with:

N_info = N_RE × Q_m × R × v

Suppose a transmission has:

• N_RE = 10,000
• Q_m = 6
• R = 0.75
• v = 2

Then:

N_info = 10,000 × 6 × 0.75 × 2

N_info = 90,000 bits

This 90,000-bit value is the unquantized information size.

The calculator then determines the appropriate TBS using its quantization procedure.

Step 2: Apply TBS Quantization

The final TBS is not simply the unquantized result. The calculator uses different calculation paths depending on whether N_info is less than or equal to 3824 bits or greater than 3824 bits.

For smaller information sizes, it uses the embedded TBS table. For larger values, it performs the corresponding quantization and code-block calculations.

Step 3: Convert TBS to Bytes

After calculating the final TBS in bits, the calculator converts it into bytes:

TBS bytes = floor(TBS bits / 8)

This provides a convenient representation of the transport block size for applications where data is expressed in bytes.

Step 4: Estimate Throughput

The calculator also provides an estimated throughput using its stated assumption of 30 kHz SCS and 2,000 slots per second:

Estimated throughput = TBS bits × 2,000 / 1,000,000

The result is displayed in Mbps.

This should be treated as a simplified estimate rather than a complete prediction of real-world 5G user throughput.

5G NR TBS Calculator Inputs Explained

Allocated Resource Elements (N_RE)

N_RE represents the number of resource elements allocated for the transmission as provided to the calculator.

The calculator accepts a value from 1 to 5,000,000.

A larger number of allocated resource elements generally provides more transmission capacity under otherwise identical conditions.

For example, consider:

• N_RE = 5,000
• Q_m = 6
• R = 0.75
• v = 2

The unquantized information size is:

5,000 × 6 × 0.75 × 2 = 45,000 bits

If N_RE is increased to 10,000 while everything else remains unchanged:

10,000 × 6 × 0.75 × 2 = 90,000 bits

The raw information size therefore doubles.

It is important to understand that the calculator treats N_RE as an input. In a detailed physical-layer calculation, determining usable resource elements may require accounting for the actual allocation and physical-layer overhead.

Modulation Order (Q_m)

Q_m represents the number of bits per modulation symbol.

Common values include:

For example, 64QAM has:

Q_m = 6

This means each modulation symbol represents six coded bits.

Increasing Q_m increases the theoretical number of bits that can be represented by the same number of modulation symbols. However, higher-order modulation generally requires better radio conditions to operate effectively.

The calculator identifies common modulation orders automatically. For example:

• 2 → QPSK
• 4 → 16QAM
• 6 → 64QAM
• 8 → 256QAM
• 10 → 1024QAM

Target Code Rate (R)

The target code rate represents the proportion of coded transmission associated with information bits in the simplified calculation.

The calculator accepts a code rate between 0.01 and 0.99.

Typical input examples include:

• 0.50
• 0.66
• 0.75
• 0.90

A code rate of:

R = 0.75

means the calculation uses 0.75 as the information-bit fraction.

For example:

N_RE = 10,000

Q_m = 6

R = 0.75

v = 2

gives:

N_info = 10,000 × 6 × 0.75 × 2

N_info = 90,000 bits

Increasing the code rate increases the calculated information size for the same resource allocation, modulation order, and number of layers.

MIMO Spatial Layers (v)

The MIMO spatial layers input represents the number of spatial transmission layers used in the calculator's model.

The calculator accepts 1 to 8 layers.

For example, consider:

• N_RE = 10,000
• Q_m = 6
• R = 0.75

With one layer:

N_info = 10,000 × 6 × 0.75 × 1

N_info = 45,000 bits

With two layers:

N_info = 90,000 bits

With four layers:

N_info = 180,000 bits

With eight layers:

N_info = 360,000 bits

This illustrates why MIMO spatial layers can have a major impact on theoretical information capacity.

However, a real 5G network cannot simply assume that eight layers are always available. The actual usable MIMO rank depends on factors such as device capability, antenna configuration, propagation conditions, and network scheduling.

3GPP TBS Quantization

One of the most important aspects of TBS calculation is quantization.

A common mistake is to calculate:

N_RE × Q_m × R × v

and assume that the resulting number is automatically the final TBS.

It is not.

The calculator first calculates N_info and then applies its implementation of the TBS determination procedure associated with 3GPP TS 38.214 Section 5.1.3.2.

The procedure uses different logic depending on the calculated information size.

TBS Calculation When N_info ≤ 3824

For smaller information sizes, the calculator uses an embedded TBS table corresponding to the range up to 3824 bits.

The calculation determines an intermediate quantized value and then searches the table for the first TBS value that is greater than or equal to that intermediate value.

The table contains standardized values beginning at:

24 bits

and continuing through:

32, 40, 48, 56, ...

up to:

3824 bits

This means the final TBS does not necessarily equal the exact raw N_info value.

For example, if the calculated intermediate information size falls between two valid TBS values, the calculator selects the applicable table entry according to its implemented procedure.

TBS Calculation When N_info > 3824

For larger information sizes, the calculator uses a different quantization path.

It first determines:

n = floor(log₂(N_info − 24)) − 5

Then it calculates:

N_info' = 2ⁿ × round((N_info − 24) / 2ⁿ)

The subsequent calculation depends on the target code rate and the resulting intermediate value.

For lower code rates, the calculator uses the applicable code-block calculation based on:

R ≤ 0.25

For higher code rates:

R > 0.25

the calculator checks whether:

N_info' > 8424

If this condition is met, it determines the appropriate number of code blocks and applies the corresponding quantization.

The purpose of these steps is to move from a theoretical information size to a TBS that follows the implemented standardized calculation procedure.

Real-Life Example: 5G NR Smartphone Download

Consider a practical scenario involving a 5G smartphone receiving a high-speed downlink transmission.

A network scheduler assigns a particular set of resources to the device. For this example, assume the calculator inputs are:

• Allocated REs: 10,000
• Modulation: 64QAM
• Q_m: 6
• Code rate: 0.75
• MIMO layers: 2

Step 1: Calculate N_info

Using:

N_info = N_RE × Q_m × R × v

we get:

N_info = 10,000 × 6 × 0.75 × 2

N_info = 90,000 bits

This is the unquantized information size.

Step 2: Determine the TBS

Because 90,000 bits is greater than 3824 bits, the calculator follows its large-TBS calculation path.

It calculates the appropriate intermediate quantized value and then applies the applicable code-block and 8-bit alignment logic.

The final result is the quantized TBS, rather than simply 90,000 bits.

Step 3: Convert to Bytes

The calculator divides the final TBS by eight and takes the integer number of bytes.

Step 4: Interpret the Result

The resulting TBS represents the information payload carried by the calculated transport block.

If the network schedules many such transport blocks every second, the aggregate data rate can become very high.

But this is where TBS and throughput must be separated.

A transport block size tells us how much information is in one transport block. It does not by itself guarantee a specific application download speed.

Real network performance depends on scheduling, physical-layer overhead, retransmissions, available resources, and other factors.

Example: Comparing 5G Modulation Schemes

The effect of modulation order can be demonstrated by keeping all other parameters constant.

Assume:

• N_RE = 10,000
• R = 0.75
• v = 2

QPSK

Q_m = 2

N_info = 10,000 × 2 × 0.75 × 2

N_info = 30,000 bits

16QAM

Q_m = 4

N_info = 60,000 bits

64QAM

Q_m = 6

N_info = 90,000 bits

256QAM

Q_m = 8

N_info = 120,000 bits

The example demonstrates the mathematical relationship between modulation order and unquantized information size.

However, higher modulation does not automatically mean better real-world performance. A network may use a lower modulation order when radio conditions are poor to maintain a more robust transmission.

Example: Comparing MIMO Spatial Layers

Now keep these parameters fixed:

• N_RE = 10,000
• Q_m = 6
• R = 0.75

Then change only the number of spatial layers.

This demonstrates the theoretical impact of spatial layers in the calculator's model.

In an actual network, the number of layers is constrained by the radio channel, UE capability, base-station configuration, antenna system, and scheduler.

Real-World Use Cases of a 5G NR TBS Calculator

5G Network Performance Analysis

Network engineers can use TBS calculations to examine how different combinations of resource allocation, modulation, code rate, and MIMO layers affect transmission capacity.

For example, an engineer can compare a 64QAM two-layer configuration against a 256QAM four-layer configuration to understand the theoretical difference in information capacity.

5G Throughput Estimation

TBS can be used as an intermediate quantity in throughput calculations.

If the size of a transport block is known and the number of transmissions per second is known, a simplified data-rate estimate can be developed.

The calculator provides an estimated throughput using its specified 30 kHz SCS assumption.

This is particularly useful for theoretical analysis and educational calculations.

MIMO Analysis

Researchers and engineers can change the MIMO layer input to study the impact of spatial multiplexing.

For example, comparing one-layer and four-layer scenarios helps demonstrate how MIMO can increase the theoretical amount of information transmitted using the same basic resource allocation.

Link Adaptation Studies

TBS calculations can also help demonstrate the relationship between modulation and coding.

When radio conditions improve, a system may be able to use a higher modulation order and/or higher code rate. When conditions deteriorate, more robust transmission parameters may be selected.

5G Education and Training

The calculator is useful for students learning:

• 5G NR
• Physical-layer concepts
• MIMO
• Modulation
• Channel coding
• Resource allocation
• Throughput calculations

Instead of performing repeated arithmetic manually, students can change one variable and immediately observe how the calculated information size changes.

5G Simulation and Software Validation

Developers working on network simulation or telecom software can use TBS calculations as a reference point when testing their own implementation.

The calculator can also help identify basic arithmetic or parameter-handling errors.

TBS vs Throughput

TBS and throughput are closely related but are not the same thing.

TBS = information bits contained in a transport block

Throughput = amount of data transmitted per unit of time

For example, a transmission might have a TBS of tens of thousands of bits. If similar transport blocks are successfully transmitted many times per second, the resulting data rate can reach hundreds of Mbps or more under suitable conditions.

However, actual throughput is influenced by much more than TBS.

Factors can include:

• Number of scheduled resources
• Slot configuration
• TDD operation
• Control signaling
• Reference signals
• Retransmissions
• Protocol overhead
• MIMO rank
• Modulation and coding adaptation
• Radio conditions
• Scheduler decisions

Therefore, the throughput output from this calculator should be considered an estimated value based on its stated assumptions, not a guaranteed real-world smartphone download speed.

Why Calculated TBS Can Differ From Actual 5G Throughput

A theoretical TBS calculation assumes a particular set of transmission parameters.

A live 5G network is dynamic.

For example, the network scheduler can change the amount of resources assigned to a UE. The modulation and coding configuration can also change as radio conditions change.

HARQ retransmissions can consume additional resources, while control and reference signals use resources that are not available for user data.

There can also be differences between theoretical resource allocation and the resources actually available to the transport block.

As a result:

Calculated TBS ≠ guaranteed application throughput

The calculator is best used for understanding and analyzing the transmission configuration represented by its inputs.

How to Use the 5G NR TBS Calculator

Using the calculator is straightforward.

Step 1: Enter Allocated Resource Elements

Enter the number of resource elements you want to evaluate.

Example:

10,000

Step 2: Enter Modulation Order

Use the appropriate Q_m value.

For example:

6 for 64QAM

Step 3: Enter Code Rate

Enter the code rate as a decimal.

For example:

0.75

Do not enter 75 for 75%.

Step 4: Enter MIMO Layers

Enter the number of spatial layers.

For example:

2

Step 5: Calculate

The calculator returns:

• Unquantized information bits
• Quantized TBS in bits
• Quantized TBS in bytes
• Modulation scheme
• MIMO spatial layers
• Estimated throughput
• Specification-compliance indicator

Common Mistakes When Calculating 5G TBS

Mistake 1: Treating N_info as Final TBS

The formula:

N_info = N_RE × Q_m × R × v

provides the unquantized information size used as an input to the TBS procedure.

It should not automatically be treated as the final TBS.

Mistake 2: Using the Modulation Number Instead of Q_m

For 64QAM, the modulation order is:

Q_m = 6

It is not:

Q_m = 64

Similarly:

• QPSK → 2
• 16QAM → 4
• 256QAM → 8

Mistake 3: Entering Code Rate as a Percentage

A 75% code rate should be entered as:

0.75

not:

75

Mistake 4: Ignoring MIMO Layers

If a transmission uses multiple spatial layers, the number of layers affects the calculator's unquantized information-size calculation.

Mistake 5: Assuming TBS Equals Download Speed

A TBS value is measured in bits per transport block.

Download speed is normally expressed in bits per second.

These are different measurements.

Mistake 6: Ignoring TBS Quantization

The raw information calculation is only one stage of the overall process. The final TBS is determined through the applicable quantization logic.

Technical Notes and Limitations

The calculator is designed around the TBS calculation logic implemented in the provided code and identifies the result as compliant with 3GPP TS 38.214 Section 5.1.3.2.

Several implementation details are important when interpreting the results.

First, the calculator accepts N_RE directly. It does not independently derive the number of usable resource elements from a complete NR physical-resource-grid configuration.

Second, the throughput calculation uses a specific assumption:

30 kHz SCS = 2,000 slots per second

Therefore, its throughput output should not be interpreted as a universal 5G NR throughput calculation.

Third, real-world network performance involves additional factors such as control resources, reference signals, scheduling, retransmissions, TDD configuration, protocol overhead, and changing MCS.

Finally, standards-based engineering work should always be checked against the applicable 3GPP specification release and the exact system configuration being analyzed.

5G NR TBS Calculator vs Manual Calculation

A manual TBS calculation requires several separate steps:

1. Calculate N_info.
2. Determine the appropriate quantization path.
3. Apply the relevant TBS table or formula.
4. Perform code-block calculations where applicable.
5. Align the result appropriately.
6. Convert bits to bytes.
7. Calculate an estimated data rate if required.

The calculator automates these steps and provides the intermediate and final results in one place.

This makes it useful for quick calculations, educational exercises, engineering sanity checks, and preliminary network analysis.

Frequently Asked Questions

What is TBS in 5G NR?

TBS, or Transport Block Size, is the number of information bits contained in a transport block for a particular NR transmission configuration. It depends on factors such as allocated resources, modulation, code rate, and MIMO layers, followed by the applicable TBS determination procedure.

How is 5G NR TBS calculated?

The calculator first determines the unquantized information size using:

N_info = N_RE × Q_m × R × v

It then applies the appropriate TBS quantization and code-block logic to determine the final transport block size.

What is the formula for 5G NR TBS?

The basic information-size calculation used by this calculator is:

N_info = N_RE × Q_m × R × v

This is an intermediate calculation. The final TBS is determined after applying the applicable quantization procedure.

What does Q_m mean in 5G NR?

Q_m is the modulation order, representing the number of coded bits per modulation symbol. Common values include 2 for QPSK, 4 for 16QAM, 6 for 64QAM, 8 for 256QAM, and 10 for 1024QAM.

What is Q_m for 64QAM?

For 64QAM:

Q_m = 6 bits/symbol

What is Q_m for 256QAM?

For 256QAM:

Q_m = 8 bits/symbol

Does increasing MIMO layers increase TBS?

Increasing the number of MIMO layers increases the unquantized information size in the calculator's model. However, real networks can only use spatial layers supported by the UE, base station, antenna configuration, radio channel, and scheduler.

Does TBS equal 5G throughput?

No. TBS represents the information bits in one transport block, while throughput measures data transmitted over time. Actual throughput depends on scheduling, resources, retransmissions, overhead, radio conditions, and other factors.

What is N_RE in 5G NR?

N_RE is the number of resource elements used as an input to the calculator's information-size calculation. It represents the allocated resource elements supplied for the transmission being evaluated.

Why is TBS quantization required?

The raw information-bit calculation does not directly represent every valid transport-block size. The calculator therefore applies its implementation of the applicable 3GPP TBS determination procedure to obtain the final TBS.

What happens when N_info is less than or equal to 3824?

The calculator uses its embedded TBS table for the N_info ≤ 3824 range and selects the applicable TBS value after calculating the required intermediate value.

What happens when N_info is greater than 3824?

The calculator uses the larger-TBS calculation path, including quantization and the applicable code-block/segmentation calculations represented in the implementation.

Key Takeaways

The 5G NR TBS Calculator provides a practical way to calculate and analyze Transport Block Size using four primary inputs: allocated resource elements, modulation order, code rate, and MIMO spatial layers.

The most important concepts are:

• N_RE determines the resource allocation used by the calculation.
• Q_m determines the number of bits per modulation symbol.
• R represents the target code rate.
• v represents the number of MIMO spatial layers.
• N_info is calculated using N_RE × Q_m × R × v.
• N_info is not automatically the final TBS.
• The calculator applies its TBS quantization procedure to obtain the final TBS.
• TBS can be expressed in both bits and bytes.
• The calculator also provides an estimated throughput using its 30 kHz SCS and 2,000-slots-per-second assumption.
• Actual 5G throughput can differ substantially from a simplified TBS-based estimate.
• For standards-critical work, the result should be validated against the applicable 3GPP specification release and complete NR transmission configuration.

Overall, TBS is a key concept for understanding how 5G NR resource allocation, modulation, coding, and MIMO combine to determine the amount of information carried by a transport block.